The present invention relates to high temperature furnaces preferably of a type employed for nuclear fuel particle coating, and more particularly to an electrode ring assembly for maintaining proper electrical contact between a heating element in the furnace and an external bus bar.
Many applications for high temperature furnaces require generally continuous or intermittent operation of the furnace over long periods of time where it is undesirable to interrupt operation of the furnace. The present invention particularly contemplates a high temperature furnace of this type employed in the coating of nuclear fuel particles. In order to protect the material forming the fuel particles, it is well known to coat them with pyrolytic carbon or metallic carbide for example. The coatings provide impermeability to retain gaseous and metallic fission products within the fuel particles. At the same time, the coatings tend to provide structural integrity even during prolonged exposure to high temperatures and irradiation conditions encountered within typical nuclear reactor operations.
A preferred method for coating nuclear fuel particles with such materials comprises the deposition of the coating material through the decomposition at high temperature of materials such as gaseous hydrocarbons. Such a coating operation is commonly performed by using a fluidized bed process to permit intimate contact between the reactant hydrocarbon gas and a bed of nuclear fuel particles. Fluidized bed coating apparatus may employ a reactor including a coating chamber arranged within a high temperature furnace of the type provided by the present invention. The necessary high temperatures are produced by one or more electrical resistive heating elements arranged within the furnace.
The furnace may commonly be formed as a cylindrical chamber with an annular arrangement of the heating elements serving to radiantly heat the interior of the furnace. The reactor may then simply be arranged within the interior of the high temperature furnace for carrying out the coating operation at a suitable high temperature.
Such a coating operation may continue over extended periods of time with temperatures in the furnace being rapidly cycled over a wide temperature range. This condition of rapid thermal cycling causes substantial expansion and contraction of electrical connections for the heating element and tends to result in loosening of the joints over a period of time. Such looseness naturally contributes to low contact pressure between the heating element and an electrode element for connecting the heating elements with a source of electrical energy. Local overheating may thus occur and eventually result in failure of the furnace to maintain proper temperature limits.
In the past, it has been necessary to interrupt operation of the furnace and cool the furnace interior in order to permit adjustments in the connections between the heating elements and electrodes. This of course has resulted in undesirable downtime which detracts from efficient operation. Also, the loosening of the contact surface may not be detected until failure of the electrode ring occurs due to overheating.
Accordingly, there has been found to remain a need for a high temperature furnace wherein proper contact may be assured and maintained between heating elements arranged within the furnace and an external bus bar supplying electrical energy to the furnace.